Levator-Sparing Oculomotor Nerve Palsy Caused by a Solitary Midbrain Metastasis

One month before death, a 63-year-old man with known lung carcinoma manifested a left third-nerve palsy and crossed ataxia. The oculomotor involvement began with a dilated left pupil and progressed to a complete left oculomotor nerve palsy, with the exception of nearly normal lid function. Pathologic examination revealed a solitary midbrain metastasis involving the left third-nerve nucleus and rootlets, with the exception of the caudal central oculomotor subnucleus and its outflow fibers.